Method of making tubular rivets



Dec. 24, 1963 A. CARUSI 3,114,921

METHOD OF MAKING TUBULAR RIVETS Original Filed Feb. 6, 1956 2Sheets-Sheet 1 A1. EXAM/D519 aka/$1,

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Dec. 24, 1963 A. CARUSI 3,114,921

METHOD OF MAKING TUBULAR RIVETS Original Filed Feb. 6, 1956 2Sheets-Sheet 2 M63 11-510. Man,

.141. EXAM/D51? Q2057,

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United States Patent 6, 1956, Ser. No. 563,435. liliapplication May 11,1959, Ser. No.

2 Claims. C1. Iii-27) This application is a division cation Serial No.563,485, filed February 6, 1956.

l The present invention relates in general to a blind rivet assemblyand, more particularly, to a method of manufacturing a tubular rivetwhich forms part of a blind rivet assembly capable of producing hi hclinching forces when set.

As general background, a blind rivet assembly of the type to which thepresent invention relates comprises a stem having thereon a tubularrivet which includes a sleeve having a head at one end and a tail at itsother end, the stem being provided at one end thereof with tail flaringmeans adjacent and engageable with the tail of the tubular rivet andbeing provided with grippable means at the other end thereof.Preferably, the stem is provided with an enlarged shank adjacent thetail flaring means and is provided with a weakened zone intermediatesuch shank and the grippable means.

In setting a rivet assembly of the foregoing general type, the assemblyis inserted through re istering holes in elements to be riveted togetherso that the tail of the tubular rivet and the tail flaring means on thestem are on one side of such elements and the head of the tubular rivetand the grippable means are on the opposite side thereof. A rivetingtool having pressure and pulling members is then applied to the rivetassembly with the pressure member seated against the head of the tubularrivet and with the pulling member in engagement with the grippable meanson the stem. The pullin member is then moved axially of the pressuremember to draw the enlarged shank of the stem into the sleeve of thetubular rivet so as to expand the sleeve into engagement with theelements to be riveted together, and to draw the tail flaring means onthe stem into tail flaring engagement with the tail of the tubularrivet, thereby clamping the elements which are to be riveted togetherbetween the head of the tubular rivet and the flared tail thereof.Eventually, the stem of the rivet assembly is broken off at the weakenedzone therein and any excess portions of the stem may be trimmed offflush with the head of the tubular rivet.

In accordance with the present invention, the external surface of thesleeve of the tubular rivet is longitud nally grooved or fissured fromthe tail of such sleeve toward the head thereof so that, as the tailflaring means on the stem is drawn into the sleeve, the sleeve is splitlongitudinally into a plurality of prongs which engage one side of theassembly of elements to be riveted together, the head on the tubularrivet engaging the opposite side thereof. The tail of the tubular rivetmay be provided with transverse notches extending from the internalsurface of the sleeve to the external surface thereof and communicatingwith the longitudinal grooves or fissures in the external surface of thesleeve. These notches facilitate initiation of the splitting of thesleeve along the longitudinal fissures in the external surface thereof,which is an important feature.

An important object of the invention is to provide a method of makingthe tubular rivet in such a manner that the prongs resulting fromsplitting of the sleeve inherently tend to curl outwardly as the sleeveis split.

Another object is to provide a method of making the of my co-pendingappli- 3,1 M321 Patented Dec. 24, 19GB tubular rivet in such a way thatthe density of the material forming the sleeve increases toward theinternal surface thereof so that, as the sleeve is divided into prongs,these prongs tend to curl outwardly as the stresses therein resultingfrom the non-uniform density are relieved.

Another object of the invention is to provide a method of forming atubular rivet of the foregoing nature from a solid bar of material whichincludes the steps of upsetting one end of the bar to form the head ofthe rivet, compacting a central zone of the bar axially of the bar fromboth ends of the bar, and subsequently drilling an axial bore throughthe bar to form the sleeve of the tubular rivet, such method alsoincluding the step of providing the external surface of the bar withlongitudinal fissures which extend from said other end thereof in adirection toward said one end thereof and which permit splitting of thesleeve into prongs upon drawing of the tail flaring means on the steminto the sleeve.

More particularly, an object of the invention is to provide a methodwherein the step of compacting the central zone of the bar of which thetubular rivet is formed includes simultaneous center punching of bothends of the bar in a direction axially of the bar, this being donesimultaneously with the upsetting of one end of the bar to form therivet head and being done after forming the external longitudinalfissures. Subsequently, an axial bore is drilled through the bar fromthe bottom of one of the recesses formed by the center punching step tothe other end of the bar to complete the forming of the tubular rivet.

The foregoing objects, advantages, features and results of the presentinvention, together with various other objects, advantages, features andresults thereof which will be evident to those skilled in this art inthe light of the present disclosure, may be attained with the exemplaryembodiments of the invention which are illustrated in the accompanyingdrawings and which are described in detail hereinafter. Referring to thedrawings:

FIGS. 1, 2, 3, 4 and 5 of the drawings illustrate successive steps ofthe method of the invention for manufacturing a tubular rivet of a blindrivet assembly;

FIG. 6 is a longitudinal sectional view of the tubular rivet;

FIG. 7 is an end elevational view of the tubular rivet, taken asindicated by the arrowed line 77 of FIG. 6;

FIG. 8 is a side elevational view of a complete blind nivet assemblyincorporating the tubular rivet made in accordance with the invention;

FIGS. 9, '10, 11 and 12 are longitudinal sectional views illustratingsue/cessive steps in the setting of the blind rivet assembly illustratedin FIG. 8 of the drawings; and

FIGS. 13, 14 and 15 are end elevational views respectively taken alongthe arrowed lines 13l3, l414 and l'15 of FIGS. 9, 10 and 12,respectively, FIG. 13 being partially in section.

Referring first to FIG. 8 of the drawings, the completed blind rivetassembly is designated generally by the numeral 20 and includes a stem22 having thereon a tubular rivet 24. The latter includes a sleeve 26having a tail 28 and a head 30 at opposite ends thereof, a sealingwasher 32 being carried by the sleeve 26 in engagement with theunderside of the head 30 for installations in which a fluid-tight sealis required. The external surface of the sleeve 26 is provided withlongitudinal fissures of grooves 34 therein which extend from the tail28 toward the head 30. The .tail v28 is provided with transverse notches36 therein which form continuations of the respective grooves 34 andwhich extend firom the external surface of the sleeve 26 to the internalsurface thereon, as best shown in- FIG. 6 of the drawings. As willbecome apparent, the purpose of the notches 36 is to facilitateinitiation of splitting of the sleeve 26 into prongs along the grooves34. The depth of the grooves 34 should not exceed approximately one-halfthe thickness of the sleeve 26. For example, for a sleeve thickness of0.40 inch, the groove depth should be approximately 0.15 inch to 0.20inch.

The stem 22 is provided at one end thereof with tail flaring means 33adjacent and engageable with the tail 28 of the sleeve 26, the tailflaring means 38 comprising an enlargement 40 on the stem having arounded, concave, annular surface 42 for tail flaring engagement withthe internal surface of the sleeve 26 as will be described. The tailflaring means 32 terminates in an enlarged shank 44 which tapers intothe body of the stem 22, as indicated at 46. Adjacent the enlarged shank44 is a weakened Zone or break neck 48 in the stem 22, this weakenedZone preferably being formed by providing the stem with an annulargroove therein. The stem 22. is provided, at the end thereof oppositethe tail flaring means 38, with grippable means 51' the means 50 beingengageable by a gripping means on the pulling member of a riveting toolto be described. While a particular form of grippable means 56 has beenillustrated, it will be understood that other types of grippable meansmay be substituted therefor.

Considering now the method of the invention of manufaoturing the tubularrivet 24, the starting material is preferably cylindrical bar stock 52,as shown in FIG. 1 of the drawings. The bar stock 52 may be of anysuitable material, aluminum being an example. As shown in FIG. 2 of thedrawings, a bar 54 is cut from the bar stock 52 as the next step in themethod of the invention.

Referring to FIGS. 3 and 4 of the drawings, the bar 54 is placed betweentwo relatively movable dies 56 and 53. In FIG. 3 of the drawings, thedies 56 and 58 are shown open without the bar 54 in place, and in FIG.4, the dies are shown closed with the bar 54 in a partially processedcondition. The die 56 is provided therein with a head-forming cavity 60and the die 58 is provided therein with a cavity 62 for forming theexterior of the sleeve 26 of the tubular rivet 24, the cavity 62 beingreferred to as a sleeve-forming cavity for convenience. The upper die 56is provided with a center punch 64 which projects into the head-formingcavity 60 in a direction axially of the sleeve-forming cavity 62, thediameter of the center punch 64 being somewhat less than the diameter ofthe sleeve-forming cavity. The peripheral wall of the sleeveformingcavity 62 is provided with ribs 66, preferably four in number, forforming the grooves 34 in the external surface of the sleeve 26 and thetransverse notches 36 in the tail 28 of the sleeve.

As will be apparent from inspection of FIGS. 3 and 4 of the drawings,when the bar 54 is placed between the dies 56 and 58 and these dies areclosed, the grooves 34 and the notches 36 are formed first and then oneend of the bar is upset to form a head 68 which approaches the finalshape of the head 30. At the same time as the head 68 is formed, thecenter punch 64 forms an axial recess 70 in the upset head 68. Also, acenter punch 72 on the die 58 projects axially into the sleeve-formingcavity 62 in alignment with the center punch 64 to form another axialrecess 74. The effect of the center punches 64 and 72 is to compact thematerial of the bar 54 axially in a central zone of the bar from bothends of the bar, the result of this increase in the density of thecentral zone being discussed hereinafter.

Referring now to FTG. of the drawings, the partly formed bar from thedies 56 and 58 is then placed in a die means comprising dies 76 and 73to complete the external forming of the tubular rivet 24. The die 76 isprovided therein with a head-forming cavity 80 conforming to the finalconfiguration of the head 30 of the tubular rivet 24. The peripheralwall of a sleeve-receiving cavity 82 of the die 78 is provided with ribs84 which correspond to the ribs 66 and which fit into the grooves 34 andthe notches 36 in the sleeve 26. The cavity 82 is provided with a centerpunch 86 which is inscrtable into the previously formed recess '74 inthe partially processed bar 54. The die 76 is provided .with a centerpunch 38 which is insertable into the previously formed recess 70 andwhich projects axially through the head-forming cavity into the cavity82 when the dies 76 and 73 are closed. The center punch 88 deepens thepreviously formed rccess '75? into a recess 93 which extends through thehead Bil and therebeyond a substantial distance.

Upon closure of the dies 76 and 78, the bar 54 assumes the configurationillustrated in FIG. 5 of the drawings. The center punches E56 and 83cooperate to further compact the material in a central zone therebctweento increase the density of the material in such zone for a purpose to bedescribed.

Referring to PEG. 6 of the drawings, an axial bore )2 is drilled fromthe bottom of the recess completely through the product resulting fromclosure of the dies 76' and '78 to form the finished tubular rivet 24.As a result of the compaction of the material of the bar 54 in a centralzone thereof by the center punches 64 and 72 and by the center punches86 and 88, the material of the final sleeve 26 will be denser adjacentthe internal surface thereof than adjacent the external surface thereof.in other words, the density of the material forming the sleeve 26increases radially from the external surface of the sleeve toward theinternal surface thereof. Consequently, the material of the sleeveadjacent the internal surface thereof will be in a state of compressionwith respect to the material adjacent the external surface of thesleeve.

Referring now to FIG. 9 of the drawings, the blind rivet assembly Zti isinserted into registering holes 94 and 96 through elements 160 and 162which are to be riveted together to form an assembly 104, FIGS. 11 and12. When the rivet assembly 20 is thus inserted into the holes 94 and96, the tail 28 of the tubular rivet 24 and the tail flaring means 23and the enlarged shank 44 on the stem 22 are disposed on one side of theassembly 104, while the head 39 of the tubular rivet and the grippablemeans 50 on the stem are disposed on the opposite side of the assembly.The washer 32, if used, under the head 3%} is cngagcable with one sideof the assembly 104.

With the rivet assembly 30 inserted through the assembly 184- in theforegoing manner, a suitable riveting tool 166 is applied to the rivetassembly 20. More particularly, the riveting tool 166 is provided with apressure member 1G3 adapted to seat on the head 30, and is provided witha pulling member which is movable axially of the pressure member andwhich is provided with gripping means 112 for gripping the grippablemeans 50 on the stem 22 of the rivet assembly. The foregoing conditionsobtaining, the pulling member 110 is moved axially of the pressuremember 108 in a direction away from the assembly 164 to pull the stem 22into the sleeve 26 of the tubular rivet 24.

Referring to FIG. 10, as the stem 22 is moved axially of the tubularrivet 24 to pull it into the sleeve 26, the enlarged shank 44 on thestern first expands the sleeve 26 to at least substantially fill theholes 94 and 96 through the assembly 164. As the tail flaring means 38engages the tail 28 of the tubular rivet 24, the sleeve 26 of this rivetsplits along the longitudinal grooves 34 in the external surface thereofto form prongs 114, intiation of the splitting action being facilitatedby the notches 36 across the tail 28 of the rivet 24. As the tailflaring means 38 forms the prongs 114, it spreads them outwardly, asillustrated in FIGS. 10 and 11, these prongs curling outwardly, as shownin FIGS. 10, 11 and 12, as they are spread. This outward curling of theprongs 114 is due in part to the action of the concave surface 42 of thetail flaring enlargement 46, but, as will be explained hereinafter, isdue primarily to the previously described compaction of the central zoneof the bar 54 in the process of forming the tubular rivet 24.Ultimately, the tail fiaring means 33 spreads the prongs 114 so that theouter ends thereof seat against one side of the assembly 164, as shownin FIG. 11, further axial movement of the stem 22 resulting in pressingthe outer ends of the prongs 114 solidly against one side of theassembly 104 to provide a very high clamping or clinching force betweenthe prongs and the head 3%, which is an important feature of theinvention.

Eventually, the resistance to axial movement of the stem 22 relative tothe tubular rivet 24 reaches a value such that it exceeds the tensilestrength of the weakened Zone 48 of the stem 22, whereupon the stembreaks at such weakened zone as illustrated in FlG. 11 of the drawings.

After rupture of the stem 22 in the foregoing manner, the stem may betrimmed off flush with the head Ell of the tubular rivet 24, as shown inPIG. 12 of the drawings, to provide a finished appearance.

Considering in more detail the outward curling of the prongs 114, partof the outward curling thereof is, as previously suggested, due to thecurling action provided by the concave tail flaring surface '42.However, the action of this surface is responsible for only a relativelysmall part of the outward curling of the prongs 134, the outward curlingof these prongs being due primarily to the hereinbefore-described mannerin which the tubular rivet 24 of the invention is formed. The outwardcurling of the prongs 114 results primarily from the compacting of thecentral zone of the bar 54 by means of the center punches 64 and 72 andthe center punches 86 and 855 in the process of forming the bar 54 intothe tubular rivet 24. What occurs during the formation of the bar 54into the tubular rivet 24 in the hereinbefore-described manner is thatthe material of the sleeve 26 is compacted more adjacent the internalsurface of the sleeve than adjacent the external surface thereof, thedensity of the material forming the sleeve thus increasing radially fromthe external surface of the sleeve toward the internal surface thereof,despite the fact that the most compacted central zone has been drilledout in forming the axial bore 92. Consequently, the material adjacentthe internal surface of the sleeve 26 is in a state of axial compressionrelative to the material adjacent the external surface of the sleeve,or, in other words, the material adjacent the external surface of thesleeve is in a state of axial tension relative to the material adjacentthe internal surface of the sleeve. Consequently, when the sleeve 26 issplit into the prongs 11 4 at the notches 36 and along the longitudinalgrooves 34, the stress differential between the interior and theexterior of the sleeve 26 is relieved, the inner surfaces of the prongs114 expanding axially and the outer surfaces thereof contracting axiallyto cause the hereinbefore-described outward curling of the prongs.

Although I have disclosed herein an exemplary embodis ment of myinvention for purposes of illustration, it will be understood thatvarious changes, modifications, and substitutions may be incorporated insuch embodiment without departing from the spirit of the invention asdelined by the claims which follow.

I claim:

1. A method of making a tubular rivet from a solid bar, including thesteps of:

(a) heading one end of said bar to form a head there- ([1)simultaneously with said heading step centrally and longitudinallypunching said bar at at least the other end thereof so as to providesaid bar with a central longitudinal zone which is in a state oflongitudinal compression relative to an annular longitudinal zone ofsaid bar located radially outwardly of said central longitudinal zonethereof;

(c) centrally and longitudinally holding said bar throughout its entirelength to internal cross sectional dimensions which are substantiallyconstant throughout the entire length of said bar and which constitutemajor portions of the corresponding external cross sectional dimensionsof said bar between said other end of said bar and said head, whereby toform a radially thin sleeve having substantially constant radialthicknesses along longitudinal lines extending from said other end ofsaid bar toward said head, the internal surface of said sleeve being ina state of longitudinal compression relative to the external surfacethereof as the result of said punching and holing steps; and

(d) simultaneously with said heading and punching steps weakening saidbar along circumferentially spaced longitudinal lines extending fromsaid other end of said bar toward said head, whereby to provide saidsleeve with circumferentially spaced longitudinal lines of weaknessalong which said sleeve is longitudinally splittable, from the free endof said sleeve toward said head, into circumferentially spacedlongitudinal prongs which tend to curl radially outwardly and thenre-versely toward said head as the longitudinal stress differentialsbetween the inner and outer surfaces of the portions of said sleevewhich form said prongs are relieved.

2. The method set forth in claim 1 wherein said holing step is aseparate and independent step comprising centrally and longitudinallydrilling said bar to a constant diameter throughout its entire lengthafter completion of said heading, punching and weakening steps.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF MAKING A TUBULAR RIVET FROM A SOLID BAR, INCLUDING THESTEPS OF: (A) HEADING ONE END OF SAID BAR TO FORM A HEAD THEREON; (B)SIMULTANEOUSLY WITH SAID HEADING STEP CENTRALLY AND LONGITUDINALLYPUNCHING SAID BAR AT AT LEAST THE OTHER END THEREOF SO AS TO PROVIDESAID BAR WITH A CENTRAL LONGITUDINAL ZONE WHICH IS IN A STATE OFLONGITUDINAL COMPRESSION RELATIVE TO AN ANNULAR LONGITUDINAL ZONE OFSAID BAR LOCATED RADIALLY OUTWARDLY OF SAID CENTRAL LONGITUDINAL ZONETHEREOF; (C) CENTRALLY AND LONGITUDINALLY HOLDING SAID BAR THROUGHOUTITS ENTIRE LENGTH TO INTERNAL CROSS SECTIONAL DIMENSIONS WHICH ARESUBSTANTIALLY CONSTANT THROUGHOUT THE ENTIRE LENGTH OF SAID BAR ANDWHICH CONSTITUTE MAJOR PORTIONS OF THE CORRESPONDING EXTERNAL CROSSSECTIONAL DIMENSIONS OF SAID BAR BETWEEN SAID OTHER END OF SAID BAR ANDSAID HEAD, WHEREBY TO FORM A RADIALLY THIN SLEEVE HAVING SUBSTANTIALLYCONSTANT RADIAL THICKNESSES ALONG LONGITUDINAL LINES EXTENDING FROM SAIDOTHER END OF SAID BAR TOWARD SAID HEAD, THE INTERNAL SURFACE OF SAIDSLEEVE BEING IN A STATE OF LONGITUDINAL COMPRESSION RELATIVE TO THEEXTERNAL SURFACE THEREOF AS THE RESULT OF SAID PUNCHING AND HOLINGSTEPS; AND (D) SIMULTANEOUSLY WITH SAID HEADING AND PUNCHING STEPSWEAKENING SAID BAR ALONG CIRCUMFERENTIALLY SPACED LONGITUDINAL LINESEXTENDING FROM SAID OTHER END OF SAID BAR TOWARD SAID HEAD, WHEREBY TOPROVIDE SAID SLEEVE WITH CIRCUMFERENTIALLY SPACED LONGITUDINAL LINES OFWEAKNESS ALONG WHICH SAID SLEEVE IS LONGITUDINALLY SPLITTABLE, FROM THEFREE END OF SAID SLEEVE TOWARD SAID HEAD, INTO CIRCUMFERENTIALLY SPACEDLONGITUDINAL PRONGS WHICH TEND TO CURL RADIALLY OUTWARDLY AND THENREVERSELY TOWARD SAID HEAD AS THE LONGITUDINAL STRESS DIFFERENTIALSBETWEEN THE INNER AND OUTER SURFACES OF THE PORTIONS OF SAID SLEEVEWHICH FORM SAID PRONGS ARE RELIEVED.